Rudolph's Pediatrics, 22nd Ed.

CHAPTER 91. Developmental Delay

Nathan J. Blum

Child development is a dynamic interaction of biologic and environmental factors. Typically, over a period of many years, an infant who is initially entirely dependent on others to meet life-sustaining needs such as food and shelter develops into an independent adult capable of caring for others. Growth of a child’s skills occurs across multiple domains of development, including motor, language, cognitive, and socioemotional domains, and allows for slowly increasing independence. Within any single domain, the sequence of new skills acquired is fairly consistent, but there is significant individual variability in the rate of development within and across the different domains that complicates attempts to distinguish children with normal variations in development from children with developmental delays. However, early detection of developmental delays is essential to promote early intervention that can improve developmental outcomes and family adjustment. During well-child care, clinicians are the professionals most likely to interact with a child early in development and thus have a unique opportunity and responsibility to detect children with developmental delays. The approach to the evaluation of developmental delay is discussed further in Chapters 185 and 547.

DEFINITIONS AND EPIDEMIOLOGY

The sequences in which children gain new skills in motor, language, cognitive, and socioemotional development are precisely delineated, and for many skills, the age at which 50% of children will be able to accomplish a specific task is known. A child’s developmental age is defined as the age at which approximately 50% of children would demonstrate similar functioning. Since developmental age is determined on the basis of the child’s functioning, it could be higher or lower than the chronological age.

A global developmental delay occurs when a child’s developmental age lags behind chronological age across all the domains of development. The degree of delay is often quantified by calculating the developmental quotient (DQ = developmental age/chronological age × 100). When a child is developing at the expected rate, the DQ is 100. However, if a 2-year-old child is functioning at a 1-year-old developmental age, the child’s DQ is 50, indicating that the child is developing at half the expected rate. A DQ less than 75 to 80 represents a significant developmental delay. When skills in one domain lag behind (or are more advanced than) skills in other domains, a dissociation in the domains of development occurs, such as seen with language disorders, coordination disorders, and learning disabilities.

Intellectual disability (formerly mental retardation) is defined as a significant deficit in both cognitive skills and adaptive functioning that develops prior to 18 years of age.¹ The deficit in cognitive skills is determined by the intelligence quotient (IQ) on a standardized IQ test that is more that 2 standard deviations below the mean. Since IQ tests are designed to have a mean score of 100 and a standard deviation of ±15 points, an IQ below 70 with a similar magnitude of deficits on tests of adaptive functioning is necessary to make a diagnosis of intellectual disability. Adaptive functioning refers to how independently and effectively an individual meets the demands of daily life compared to what is expected for his or her age. It is critical to recognize that factors other than cognitive skills effect adaptive functioning. For instance, an individual’s behavior, motivation, social skills, and education will effect adaptive functioning, as will the opportunities, demands on the individual, and supports available to assist the individual.

The importance of adaptive functioning is further highlighted by the epidemiology of intellectual disability. Approximately 1.5% of school-aged children in the United States are diagnosed with intellectual disability compared to approximately 1% of adults.^2,3 Children may be diagnosed with intellectual disability because they struggle with the academic demands of school, and the diagnosis may help provide access to special education services. Once out of school, if the individual is employed, living independently, and socially successful, he or she may no longer demonstrate the deficits in adaptive functioning required for the diagnosis.³

Intellectual disability is often further sub-classified on the basis of IQ test score: mild intellectual disability (IQ: 50–55 to 70); moderate intellectual disability (IQ: 35–40 to 50–55); severe intellectual disability (IQ: 20–25 to 35–40); profound intellectual disability (IQ: below 20–25).⁴ At the boundaries, the IQ scores overlap to account for the fact that individuals with similar IQ scores can differ significantly in their functioning (eTable 91.1).

Increased recognition that the level of adaptive functioning is significantly affected by environmental conditions and support available to assist individuals and by the stigma associated with the term mental retardation led to a change in the name to intellectual disability in 2007. Intellectual disability and mental retardation are currently both used to describe the same disability.

ETIOLOGY AND GENETICS

Across the spectrum of cognitive impairments, the influences of biologic and psychosocial factors is not uniform. The brain requires appropriate stimulation in order for development to proceed (see Chapter 81). Children living in poverty, who are more likely to experience poorer schooling, less responsive parenting, and other psychosocial stressors, are at increased risk for cognitive impairments, particularly milder range impairments.⁵ Genetic abnormalities are the most commonly identified biologic abnormality found to cause intellectual disability (see Chapter 185).

Prenatal or postnatal injury to the developing brain can also cause intellectual disability. Low birth weight (<1500 grams) is associated with a 3-fold increase in the risk of intellectual disability. In utero alcohol exposure is the most common teratogen exposure known to cause intellectual disability.⁶ Congenital infections, postnatal infections such as encephalitis or meningitis, and traumatic brain injury cause a small percentage of cases of intellectual disability.

CLINICAL FEATURES AND DIFFERENTIAL DIAGNOSIS

Children with developmental delays are seen by pediatricians for a variety of reasons. Most commonly, parents are concerned that the child is not meeting age-appropriate expectations for development. In other cases, parents may be concerned about behavioral difficulties, problems with peer interactions, or poor school performance. It is important for pediatricians to consider a developmental delay during all these clinical encounters.

Early identification of children with developmental delays is easier for more severe delays. Children with severe delays are likely to be detected in the first 6 months of life when they may be noticed to have difficulty tracking visual stimuli and responding consistently to auditory stimuli. They may have difficulty sucking and feeding, abnormalities in muscle tone, and/or a delay in smiling at caregivers, rolling over, or sitting.

Children with less severe delays may be brought to the pediatrician during the second and third years of life due to lack of attainment of language milestones. This creates a challenge for pediatricians in distinguishing children with global developmental delays who are at high risk for intellectual disability from the more prevalent language disorders (see Chapter 86). Finally, quite a few children with mild intellectual delays are not detected until they are having difficulty in school.

A delay in language development is often the main concern of parents of a child with both a global delay and an isolated language delay. Many children with mild delays may not be brought to the physician’s attention by parents. Developmental screening tests for early detection of delays are now a standard of care during pediatric health supervision visits (see Chapter 82 and Table 82-1).

When children are found to be developmentally delayed, the clinician should consider possible causes other than intellectual disability. The possibility of a language disorder has been discussed. It is particularly important for physicians to consider the possibility of a hearing or vision deficit because these deficits may interfere with development and require specific interventions. In addition, motor delays (eg, children with cerebral palsy) may interfere with performance on a developmental test and not allow a child to demonstrate their true cognitive potential. Autism spectrum disorders interfere with communication and social interaction in a manner that often makes accurately assessing cognitive ability particularly challenging (see Chapter 92).

In assessing the result of a developmental screening test, psychosocial, cultural, and behavioral factors also must be considered. Beliefs about when children should attain milestones such as toilet training, knowing colors, and putting on shoes can vary significantly among cultures and influence when children attain these milestones.⁷ Assessing a child raised in a bilingual environment in only the culture’s dominant language may unfairly limit performance. Finally, young children’s performance on a test may be affected by anxiety, fatigue, hunger, illness, or oppositional behavior.

Table 91-1. Risk Factors for Developmental Delay

DIAGNOSTIC EVALUATION

The child’s medical history may suggest an increased risk for developmental delays. Infants with risk factors need to be monitored closely (see Table 91-1). Careful attention should be paid to the family history. The inquiry should not be limited to diagnosed disabilities but also should ask about relatives who struggled in elementary school or did not learn to read. Specific aspects of the physical examination may provide a clue to the etiology of developmental delay.

Brain growth is the principle stimulus for increasing head circumference, and an unusually small or large head circumference may suggest an abnormality of brain development, particularly if the small or large head size is not a family trait (see Chapter 185 and 550). The presence of dysmorphic features may suggest the presence of specific genetic syndromes or at least a prenatal onset of the disorder. The skin should be evaluated for signs of a neuro-cutaneous syndrome, such as neurofibromatosis (café au lait spots) tuberous sclerosis (hypopigmented macules), or Sturge-Weber syndrome (facial hemangiomata). A Woods lamp examination may assist in the visualization of hypopigmented macules characteristic of tuberous sclerosis. The neurological examination may demonstrate abnormalities of muscle tone or focal signs that may be helpful in evaluating the etiology for the developmental delay. An infant with hypotonia and developmental delays should be evaluated for Down syndrome or Prader-Willi syndrome. An infant with abnormalities in strength and tone in a hemiplegic pattern may have had a fetal stroke, whereas abnormalities in strength and tone in a diplegic or quadriplegic pattern may suggest hypoxic-ischemic brain injury.

Hearing and vision should be evaluated in all children with developmental delays. Sensory deficits in these areas can cause developmental delays and require specific types of interventions. Moreover, children with intellectual disability are at an approximately 10-fold higher risk of having hearing and vision deficits when compared to the general population. Failure to recognize and remediate these deficits will limit the effectiveness of early intervention.

Only about 20% to 30% of children with global developmental delays will have findings on the history or physical examination that suggest a specific diagnosis.⁸ When a comprehensive history and physical examination do not suggest an etiology, additional tests should be considered. These include tests to evaluate the child for a genetic etiology, metabolic etiology, and neuroimaging. Before embarking on extensive investigations, the clinician should discuss with the family the information that the evaluation may provide. Making a genetic diagnosis may provide some information about the prognosis, information about the risk of recurrence, and information about associated conditions for which the child should be monitored and screened. For example, children with Down syndrome are screened regularly for hypothyroidism. However, it is not likely that a genetic diagnosis will change the recommended interventions for or outcome of the child’s cognitive deficits. In addition, genetic tests can suggest that family members not involved in the decision to test the child are also at increased risk of having a child with a cognitive disability. When metabolic disorders are diagnosed early, interventions can often prevent the cognitive deficits, but once the brain injury has occurred, treating the metabolic condition does not usually result in significant improvements in cognitive functioning.

Consensus guidelines recommend that the genetic evaluation of children with an intellectual disability include a high-resolution karyo-type and testing for Fragile X syndrome.^6,12 The diagnostic yield from these tests is reported to be between 3% and 10%. Microarray-based comparative genomic hybridization can detect chromosomal abnormalities in 5% to 17% of individuals with normal results on a high-resolution karyotype. Structural brain abnormalities can be detected using magnetic resonance imaging in 10% to over 50% of individuals with intellectual disability depending on the severity of the intellectual disability and the setting from which patients are recruited.⁶ Brain imaging should be performed in patients with significant microcephaly, macrocephaly, seizures, loss of skills, or focal neurological deficits. In other situations, the value of brain imaging is more controversial. Inborn errors in metabolism are a rare but important cause of intellectual disability because specific therapies to avoid brain injury and metabolic decompensations may be available. Newborn screening for some metabolic disorders occurs in all states, but there is variability among states in the number of disorders and the specific disorders that are screened. Indications for metabolic testing are shown in Table 91-2 and Figure 185-1. If there is a strong suspicion of a metabolic disorder, referral to a metabolic specialist is appropriate.

MANAGEMENT AND TREATMENT

When a pediatrician sees a child with a developmental delay, the first decision the physician must make is whether to recommend further observation or to refer for evaluation and intervention. Although some children, particularly boys, under 2¹/₂ years of age with isolated and mild delays in expressive language have a maturational lag and will often catch up without intervention, children with delays in expressive and receptive language or global delays are at high risk for ongoing difficulties and should be referred for further assessment and intervention.^14,15

Table 91-2. Indications for Metabolic Testing

Once the decision is made to refer the child, the pediatrician’s role includes helping the family to obtain appropriate services for the child, providing initial support and ongoing guidance as the family adjusts to the diagnosis and challenges of raising a child with a cognitive disability, and considering the etiologic evaluation and any unique health maintenance needs associated with a specific genetic or metabolic disorder.

Discussing a child’s developmental delays with parents is as difficult as discussing the diagnosis of any life-altering chronic disease. Many parents experience significant grief reactions related to the loss of their dreams for their child’s future. The physician should recognize that denial or anger is often a predictable part of a grief reaction. The focus of the initial discussion should include the concrete steps parents need to take to help their child, including how to obtain early intervention services. Furthermore, the clinician can play a critical role in emphasizing strengths they see in the child and family and helping the parents promote the child’s development. Throughout childhood, the pediatrician can support parents as they work with early intervention providers and schools to recognize that in all but the most severe disabilities, the focus of intervention should be on assisting the child in obtaining skills that will maximize the child’s independence in daily living, social interactions, and academic/work environments.

Federal legislation, most recently reauthorized as the Individuals with Disabilities Education Improvement Act (IDEA) of 2004, has made early intervention services available in virtually every community in the United States. For children 0 to 3 years of age, an Individualized Family Service Plan (IFSP) is developed by a multidisciplinary team that includes the parents. The multidisciplinary team can provide assessments of the child’s development and socioemotional functioning as well as family resources and needs. The services that are allowed under the law are quite extensive, including physical, occupation, and speech therapies; family training; psychological counseling; home visits; social work services; and assistive technology.¹⁶

Early intervention for children with developmental delays is critical for improving outcome, particularly for those with additional psychosocial risk factors. Studies of early intervention programs consistently demonstrate benefits, including improved academic performance, less grade retention, less use of special education, and improved high school graduation rates.¹⁷

For individuals 3 to 21 years of age, IDEA guarantees the individual a free appropriate public education in the least restrictive environment. A multidisciplinary team that includes professionals in the school and the child’s parents develop an individualized educational plan (IEP).¹⁸ The IEP should include a statement of the measurable annual goals for the child’s education and a statement of the special education services that will be provided to help the child reach these goals. Supplementary aids and accommodations needed for the child to be successful should be specified. Physicians can help parents to understand that the law makes them equal partners with school personnel in determining what is needed to help their child be successful. Parents should think about what their child needs prior to the initial meeting to develop the IEP and request these services. If parents and the school cannot agree, the law mandates a hearing process to assure that students’ and parents’ rights are respected.

NATURAL HISTORY AND PROGNOSIS

The outcome for individuals with intellectual disability is diverse. Except at the extreme lower end of possible IQ scores, IQ alone is not a good predictor of outcome. The individual’s IQ interacts with associated medical, developmental, behavioral, and emotional conditions; the individual’s social skills and other capabilities; and family and community supports to determine outcome. Almost all individuals with an intellectual disability will require assistance in school with a focus on each student’s relative strengths and weaknesses. As adults, many individuals with IQs less than 70 can have functional math and literacy skills, live independently, and be employed.¹⁹ They may require periodic assistance, particularly during periods of stress or change.

Individuals with more significant impairments may live at home or in a supervised setting in the community. They may be able to work in the community through the supported employment process. A job coach, often provided by a state’s vocational rehabilitation services, trains the individual to perform a specific job in a community setting. Individuals with the most severe impairments may need to be employed in a supervised employment setting, often referred to as a sheltered workshop, specifically designed for individuals with disabilities.